NO20120362A1 - Radiation-induced, stiffenable mixture and method using the same - Google Patents

Description

The present invention relates generally to hydrocarbon exploration and production, such as underground cementing operations, and more particularly to compositions and methods that allow greater control over the solidification of fluids or slurries used in such operations.

Background

Natural resources such as oil and gas located in an underground formation can be extracted by drilling a well down to the underground formation, typically while circulating a drilling fluid in the well. After the well has been drilled, a string of pipes, e.g. casing, driven into the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus between the outside of the pipe and the walls of the wellbore, although other methodologies are known in the art.

Hydraulic cement mixtures are in common use during drilling, completion and repair of oil and gas wells. For example, hydraulic cement mixtures are used in primary cementing operations whereby strings of pipe such as casing or extension pipe are cemented into wellbores. When carrying out primary cementing, a hydraulic cement mixture is pumped into the annulus between the walls of a wellbore and the outer surface of a pipe string placed in the same. The cement mixture is allowed to solidify in the annulus to thereby form an annular mantle of hardened, substantially impermeable cement. This cement mantle provides physical support for and positions the pipe string in relation to the walls of the wellbore and binds the outer surface of the pipe string to the walls of the wellbore. The cement mantle prevents the unwanted migration of fluids between zones or formations penetrated by the wellbore. Hydraulic cement mixtures are also in common use to plug lost circulation and other zones with unwanted inflow and outflow of fluids in wells, to plug cracks and holes in pipe strings cemented in the same and to perform other required auxiliary operations in wells. After the cement is placed in the wellbore, the wellbore requires a period of time for the cement to harden and achieve sufficient mechanical strength to resume drilling operations. This downtime is often referred to as "waiting-on-cement/waiting-on-cement" or WOC. If operations are resumed before the cement achieves sufficient mechanical strength, the structural integrity of the cement may be compromised.

Two common pumping methods have been used to place the cement mixture in the annulus. The cement mixture can be pumped down the inside diameter of the casing and up through the annulus to the desired position. This is referred to as the conventional circulation method. Alternatively, the cement mixture can be pumped directly down the annulus to in this way displace well fluids present in the annulus by pushing them up and into the inner diameter of the casing. This is referred to as the reverse circulation method. Cement can also be used inside the well in other ways, such as by placing cement inside the wellbore at a desired position and sinking a string of casing into the cement. The latter method can, for example, be used where it is not possible to circulate well fluids due to fluid loss into a formation penetrated by the wellbore.

When carrying out primary cementing as well as preventive cementing operations in boreholes, cement mixtures are often exposed to high temperatures, especially when the cementing is carried out in deep underground zones. These high temperatures can shorten the thickening time of the cement mixtures, which means that solidification of the cement occurs before the cement is sufficiently pumped into the annulus. It has therefore been required to use solidification-retarding additives in the cement mixtures. These additives extend the setting time of the mixtures so that sufficient pumping time is provided to place the cement in the desired position.

While it has been developed using a number of known retarder additives for cement, such as sugar or sugar acids, unpredictable results can occur. Hydroxycarboxylic acids, such as tartaric acid, gluconic acid and glucoheptonic acid, are in common use in oil well cementing as a cement retarder. If an excess of hydroxycarboxylic acid is used, however, it can over-retard the solidification of the cement slurry and thereby cause it to remain fluid for a longer period of time. This over-retardation can lead to extended waiting time before drilling can be resumed and can allow gas to invade the slurry thereby causing unexpected gas migration. This extended waiting time results in delays in subsequent drilling or completion activity.

In a number of cementing applications, water-based salt has been used as an additive in cementing mixtures. The salt, generally sodium chloride, serves as a dispersant in the cement slurry and causes the slurry to expand upon solidification, thereby improving the achievement of a good bond between the wellbore and the casing upon solidification of the slurry. However, salt-saturated slurries can cause problems for boundary formations and in certain situations salt such as calcium salt can act as an accelerator, reducing the setting time of the cement mixture in an attempt to overcome the negative effects of setting retarders. However, the presence of a setting and strength-accelerating agent, such as calcium salt, in the cement mixture may increase the risk that the cement mixture may thicken or solidify before placement. Given the complexity of cement chemistry and the large temperature and pressure gradients that exist in the wellbore and the problems of predicting the exact downhole temperatures during placement and solidification of the cement, it can be difficult to control the retarder additive and accelerator to achieve the desired solidification behavior. Systems are generally oversized to have a very long setting time (or thickening time) to ensure that the mix remains fluid until all cementitious material is in place which can lead to excessively long WOC.

There is therefore a need for improved procedures for regulating solidification, which provide predictable solidification times for cement mixtures in underground environments that exist in wells. It is particularly desirable to develop methods for cement-based systems with rapid solidification whereby the timing of solidification is under the control of technicians in the field without the risk of premature solidification. There is consequently a need for a procedure for cementing a wellbore which will simultaneously contain sufficient retarder material to ensure suitable pumpability for the desired pumping duration and a sufficient concentration of an accelerator to shorten the solidification time, whereby the thickening effect of the accelerator is under the control of technicians in the field .

Summary of the invention

The present invention is generally related to well fluids and/or slurry mixtures which allow greater control over solidification of such mixtures in a wellbore.

According to one aspect of the present invention, there is provided a method for use in a wellbore which comprises: deploying a mixture in an underground formation after drilling the wellbore therein; and exposing the mixture to ionizing radiation.

In another aspect, there is provided a composition comprising: a well treatment fluid; and a solidification modifier; whereby the solidification modifier is capable of degrading upon exposure to ionizing radiation.

In another aspect, there is provided a method for isolating a part of a wellbore comprising: deploying a sealing compound in an underground formation after drilling the wellbore therein; and exposing the sealing compound to ionizing radiation.

In another aspect, there is provided a method for cementing a wellbore comprising: preparing a cement mixture comprising: hydraulic cement, sufficient water to form a slurry, and a setting retarder; place the cement mixture in

the well hole; and exposing the slurry to ionizing radiation to degrade the solidification retarder.

In another aspect, there is provided a method for cementing a wellbore comprising: preparing a cement mixture comprising: hydraulic cement, sufficient water to form a slurry, a solidification retarder and an additive selected from the group consisting of an accelerator, a oxidizing agent and a combination thereof; deployment of the cement mixture in the wellbore; and exposing the slurry to ionizing radiation to separately or in combination deactivate the solidification retarder, activate the accelerator, or release the oxidizing agent.

In another aspect, there is provided a sealing composition comprising: a well treatment fluid; and a solidification modifier; whereby the solidification modifier is capable of degrading upon exposure to ionizing radiation.

In another aspect, there is provided a cement mixture comprising: hydraulic cement; water; and an accelerator or oxidizing agent, or both, whereby the accelerator and/or oxidizing agent is combined with at least one polymer component; whereby the polymer component is capable of degrading upon exposure to ionizing radiation.

In another aspect, there is provided a cement mixture comprising: hydraulic cement; water; and a sensitized retarder; and an accelerator combined with a polymer component; whereby the sensitized retarder and polymer component are capable of degrading upon exposure to ionizing radiation.

In another aspect, there is provided a cement mixture comprising: hydraulic cement; water; and a sensitized retarder; whereby the sensitized retarder is capable of degrading upon exposure to ionizing radiation.

A procedure is described here for isolating part of a wellbore by producing a sealing mixture that includes a solidification modifier. The sealing compound is placed into a well hole and exposed to ionizing radiation to change the solidification modifier. The altered setting modifier serves to increase the mechanical strength of the sealing compound.

A mixture is described here for isolating a part of a wellbore by preparing a sealing mixture with a well treatment fluid and a solidification modifier. The sealing compound is placed in a well hole and exposed to ionizing radiation to change the solidification modifier. The modified setting modifier serves to increase the mechanical strength of the sealant compound. The solidification modifier may have a radiation tolerance of less than 500 KiloGray.

The sealing mixture may have one or more components selected from the group consisting of sealants, resins, cement, sludge with the ability to solidify, structural fluids and combinations thereof. The setting modifier may include one or more ingredients selected from an accelerator, an oxidizing agent, a setting retarder, or combinations thereof and may include a polymer component. The ionizing radiation can cause degradation of the polymer component. The polymer component can form an encapsulating layer over particles in the solidification modifier. The polymer component may be mixed with the solidification modifier so that the polymer component serves as a binder and the resulting mixture may then be formed into a pellet. The polymer component can form an encapsulating layer over the pellet.

The polymer component can have a radiation tolerance of less than about 500 KiloGray and can be selected from the group consisting of polyisobutylene, fluoroelastomers, silicone rubber, polyesters, polytetrafluoroethylene, polyacetals, polypropylene, copolymers of polypropylene-ethylene, polymethylpentene, polymethyl methacrylate, fluorinated ethylene propylene and combinations thereof.

The setting modifier may include an accelerator in an amount from about 0.1% to about 20% by weight of the sealant composition. When the sealing compound is exposed to ionizing radiation, the accelerator can be enabled to react with compounds in the sealing compound to increase the mechanical strength of the sealing compound.

The setting modifier may also include an oxidizing agent in an amount of from about 0.05% to about 5% by weight of the sealing composition capable of attacking any setting retarder. By exposing the sealing compound to ionizing radiation, one can enable the release of the oxidizing agent which reduces the retarder's effect and allows solidification.

The setting modifier may include a setting retarder in an amount from about 0.1% to about 10% by weight of the sealant composition. The setting modifier may be a sensitized retarder and may be a boronated compound. The ionizing radiation may be sufficient to degrade the solidification retarder in order to reduce the retarder effect in this way.

The method and composition may additionally include at least one sensitizing material to increase the sealing composition's ability to capture the ionizing radiation. The sensitizer material may be a boron compound. The sealing mixture may additionally include at least one scintillator material capable of emitting secondary radiation upon exposure to the ionizing radiation. The sensitizer material can also be a scintillator material.

The ionizing radiation can be selected from the group consisting of alpha radiation, beta radiation, gamma radiation, neutron radiation, proton radiation, UV radiation and X-ray radiation. The ionizing radiation may be emitted from a high flux neutron source selected from the group consisting of plutonium-beryllium, americium-beryllium and americium-lithium. The high flux neutron source can be an accelerator-based neutron generator.

A radiation emitter can be lowered into the wellbore and the ionizing radiation can be emitted from a radiation emitter that is subject to the control of technicians. Two or more radiation emitters can optionally be lowered separately to two or more depths in the wellbore so that the relevant depths in the wellbore can be exposed to ionizing radiation at the same time.

An alternative method is a method of cementing a wellbore which includes preparing a cement mixture including a hydraulic cement and a sufficient amount of water to form a slurry, adding an accelerator to the slurry, placing the slurry containing the accelerator in a wellbore, and subjecting the slurry to ionizing radiation after the slurry is pumped into the wellbore to activate the accelerator. The accelerator may be a calcium salt. The accelerator can be combined with a polymer component, such as mixed where the polymer component serves as a binder and the resulting mixture is then formed into a pellet. The ionizing radiation can cause degradation of the polymer component and promote release of the accelerator. The accelerator can be added in an amount from about 0.1% to about 20% of the weight of the cement. The polymer component may have a tolerance for ionizing radiation of less than about 500 KiloGray. The ionizing radiation can be emitted from a high-flux neutron source.

An alternative embodiment is a procedure for cementing a wellbore which includes producing a cement mixture with an accelerator agent, whereby the accelerator agent is encapsulated by a polymer, placing the cement mixture into the wellbore and exposing the deployed cement mixture to ionizing radiation. The polymer serves to isolate the accelerator from the cement mixture. The step of introducing the ionizing radiation is sufficient to induce the degradation of the polymer to thereby disperse the encapsulated

the accelerator in the cement mixture.

An alternative embodiment is a method of cementing a wellbore which includes preparing a cement mixture with an oxidizing agent and a retarder, whereby the oxidizing agent is encapsulated by a polymer but where the retarder is not, placing the cement mixture in the wellbore and exposing the deployed cement mixture to the ionizing the radiation. The polymer serves to isolate the oxidizer from the cement mixture and the retarder contained therein. The step of applying the ionizing radiation is sufficient to induce the degradation of the polymer to thereby disperse the encapsulated oxidant in the cement mixture and then degrade the retarder to thereby solidify.

There is also described here a procedure for cementing a wellbore which includes the production of a cement mixture with a retarder. The cement mixture is placed in a well hole and the deployed cement mixture is exposed to ionizing radiation from a neutron source. The radiation that is supplied to the cement mixture has sufficient strength to cause selective change or degradation of the molecules in the retarder in order in this way to allow hardening operations to take place in the cement. In one embodiment, the retarder is a sensitized retarder, such as a boronated retarder.

Also described herein is a method for cementing a wellbore which includes preparing a cement mixture that includes an accelerator and a retarder, placing the resulting cement mixture in a wellbore and exposing the deployed cement mixture to ionizing radiation of sufficient strength to cause selective change or degradation of the molecules in the retarder in order in this way to allow the accelerator agent to have an effect seam results in rapid hardening of the cement mixture. In an optional embodiment, the method includes preparing a cement mixture by first adding an accelerator to the mixture including cement, water and a sensitized retarder. In an alternative embodiment, the accelerator is encapsulated in a polymer capsule, which serves to isolate the accelerator from the cement mixture. The step of introducing the ionizing radiation may be sufficient to induce the degradation of the polymer capsule to thereby disperse the encapsulated accelerator in the cement mixture.

Also described here is a cement mixture which includes cement particles, water and at least one additive. In one embodiment, the additive is selected from the group consisting of a sensitized retarder, a polymer-encapsulated accelerator, an accelerator mixed with a polymer and formed into a pellet, an accelerator mixed with a polymer and formed into a pellet which is then coated with a polymer, and combinations of this.

The foregoing has roughly provided an introduction to the features and technical advantages of the present invention so that the detailed description of the invention can be more easily understood. The features and technical advantages of the present invention will be apparent to those skilled in the art upon study of the detailed description of the embodiments of the invention hereinafter.

Brief description of the figures

Figure 1 illustrates a cross-section of a well seen from the side.

Figure 2 is a diagram of polymer brittleness due to neutron irradiation for films of different materials and thicknesses. Figure 3 is a diagram of gas penetration for two polymer films of different thickness when exposed to neutron radiation. Figure 4 is a diagram of conductivity illustrating the delayed release of an encapsulated material upon exposure to radiation.

Detailed description

The present invention is generally related to well operations involving fluids or slurries, and more specifically fluids or slurries containing accelerator agents and/or retarders that can be released, activated and/or deactivated on command to effect thickening of the fluid or slurry. The fluids or slurries referred to herein may be any suitable for well operations, drilling, completion, overhaul or production operations such as cement, drilling mud, lost circulation fluids, fracturing fluids, structural fluids, sealants, resins, etc. One embodiment of the present invention relates to cementing operations for wells and more specifically to procedures for cementing wellbores using cementitious mixtures containing accelerators and/or retarders that can be released and/or deactivated on command.

The cementitious compositions described herein generally include water and a cementitious component such as hydraulic cement, which may include calcium, aluminum, silicon, oxygen and/or sulfur which solidifies and hardens upon reaction with the water.

With reference to Figure 1, a cross-section of an embodiment of a well hole 2 is shown seen from the side. Surface casing 4, with a wellhead 6 attached thereto, is installed in the wellbore 2. The casing 8 hangs from the wellhead 6 to the bottom of the wellbore 2. An annulus 10 is defined between the casing 8 and the wellbore 2. A flow line 12 in the annulus communicates with the annulus 10 through the wellhead 6 and/or the surface casing 4 with an annulus valve 14. The flow line 16 is connected to the wellhead 6 to allow fluid communication with the inner diameter of the casing 8 and a casing valve 18. At the lower end of the casing 8, the casing is open to the wellbore 2 or has circulation openings in the walls of the casing 8 (not shown) to allow fluid communication between the annulus 10 and the inner diameter of

casing 8.

A fluid mixture, such as a cement mixture, can be pumped down the casing 8 and circulated up the annulus 10 while fluid return is taken from the annulus 10 out flow line 12 in a typical circulation direction. Alternatively, the cement mixture can be pumped into the annulus 10 from a flow line 12 while fluid return is taken from the inner diameter of the casing 8 through the flow line 16. In this way, fluid flows through the well 2 in a reversed circulation direction.

The casing may be a drill string after the completion of the drilling operations. The drilling fluid can be circulated out of the wellbore and replaced with another drilling fluid, completion fluid, cement slurry and the like.

In an alternative method, a fluid mixture, such as a cement slurry, can be placed in the wellbore 2 and a sealed or filled pipe, such as a casing pipe 8, can be lowered into the well 2 so that the fluid mixture is displaced into the annulus area 10 in order in this way to place the fluid mixture inside the annulus 10 without pumping the fluid mixture into the annulus 10. The procedure described above can be termed "puddle" cementing. The fluid mixture can be a drilling fluid placed inside the wellbore after the drilling operations have been completed.

Any cement suitable for use in underground applications may be suitable for use in the present invention. In certain embodiments, the cement compositions used in the present invention include hydraulic cement. Examples of hydraulic cement include, but are not limited to, Portland cement (e.g., Class A, C, G, and H Portland cement), pozzolan cement, gypsum cement, phosphate cement, high alumina cement, silica cement, high alkalinity cement, and combinations thereof . The cement includes shale, cement kiln dust or slag from incinerators may include vitrified shale; in certain other embodiments, the shale may include raw shale (eg, unburnt shale) or a mixture of raw shale and vitrified shale.

The cementitious compositions used in the present invention generally include a base fluid. There is a wide variety of base fluids that may be suitable for use with the present invention including, among others, a water-based base fluid, a non-aqueous base fluid, and mixtures thereof. Where the base fluid is water-based, it may include water which may come from any source, provided the water does not contain any excess compounds (eg dissolved organic matter, such as tannic acids) which may adversely affect other compounds in the cement mixtures. For example, a cement mixture useful with the present invention may include fresh water, salt water (eg, water containing one or more salts dissolved therein), brine (eg, saturated salt water), or sea water. Where the base fluid is non-aqueous, the base fluid may include any number of organic liquids. Examples of suitable organic liquids include but are not limited to mineral oils, synthetic oils, esters and the like. In certain embodiments of the present invention where primary cementing is performed, a water-based base fluid may be used. The base fluid may be present in an amount sufficient to form a pumpable slurry. Specifically, in certain embodiments where the base fluid is water, the base fluid may be present in the cement compositions used in the present invention in an amount ranging from about 25% to about 150% by weight of cement ("bwoc"). In certain embodiments where the base fluid is water, the base fluid may be present in the cement mixtures in the range of from about 30% to about 75% bwoc. In other embodiments where the base fluid is water, the base fluid may be present in the cement mixtures in the range of from about 40% to about 60% bwoc. In other embodiments where the base fluid is water, the base fluid may be present in the cement mixtures in the range of from about 35% to about 50% bwoc. The cement mixtures may include a sufficient amount of water to form a pumpable cementitious slurry. The water can be fresh water, e.g. unsaturated water-based salt solution or a saturated water-based salt solution such as brine or seawater.

The fluid or slurry mixtures used in the present invention may optionally include a fluid loss control additive. A variety of fluid loss control agents may be suitable for use with the present invention, including but not limited to fibers, flakes, particles, modified sugars, latexes, and acrylamide-methyl-sulfonic acid copolymers such as those described in US Patent 4,015,991; 4,515,635; 4,555,269; 4,676,317; 4,703,801; 5,339,903 and 6,268,406. Generally, the fluid loss control additive is present in the cement mixtures used with the present invention in an amount sufficient to provide a desired degree of fluid loss control. More specifically, the fluid loss control additive may be present in the cement mixtures used in the present invention in an amount ranging from about 0.1% to about 10% bwoc. In certain embodiments, the fluid loss control additive is present in the cement compositions used in the present invention in an amount ranging from about 0.2% to about 3% bwoc.

Optionally, the cementitious mixtures used in the present invention

also include a modifier for mechanical properties. Examples of suitable modifiers for mechanical properties may include gases that are added at the surface (for example, nitrogen), gas-generating additives that can generate a gas in place at a desired time (for example, aluminum powder or azodicarbonamide), hollow microspheres, elastomers ( for example, elastic particles comprising a styrene/divinylbenzene copolymer), materials with a large length/width ratio (including but not limited to fiber), elastic graphite-containing materials, vapor/fluid-filled spheres, matrix-sorbable materials with time-dependent sorption (initiated by for example degradation), mixtures of these (for example mixtures of microspheres and gases), or equivalent. In certain embodiments of the present invention, the optional mechanical property modifier may include a latex.

In certain optional embodiments where microspheres are added to well treatment fluid compositions, or a fluid or slurry, such as cement compositions useful for the present invention, the microspheres may be present in the cement compositions in an amount ranging from about 5% to about 75% bwoc. In certain embodiments of the present invention, the inclusion of microspheres in the cement compositions useful with the present invention can reduce the density of the cement composition.

In certain optional embodiments where one or more gas-forming additives are used as modifiers for mechanical properties in the fluid or slurry mixtures used in the present invention, said one or more gas-forming additives may include, among other things, aluminum powder that can generate hydrogen gas on site, or they may include azodicarbonamine which can generate nitrogen gas on site. Other gases and/or gas-generating additives may also be suitable for inclusion in the fluid or slurry mixtures used in the present invention. When included, a gas-generating additive may be present in the cement mixtures in an amount ranging from about 0.1% to about 5% bwoc. In certain embodiments where the gas-generating additive is aluminum powder, the aluminum powder may be present in the cement mixtures in an amount from about 0.1% to about 1% bwoc. In certain embodiments where the gas-generating additive is an azodicarbonamide, the azodicarbonamide may be present in the cement compositions in an amount ranging from about 0.5% to about 5% bwoc.

The fluid or slurry mixtures used in the present invention may optionally also include additional suitable additives including antifoam agents, dispersants, density reducing additives, surfactants, weight materials, viscosity regulating agents, fly ash, silica, agents for regulating free water and the like. Any suitable additive may be incorporated into the fluid or slurry compositions used in the present invention.

The fluid or slurry mixtures used in the present invention may additionally include a solidification retarder. When solidification retarders are mixed in, the time that the fluid or slurry mixture remains a fluid is extended. These retarder mixtures therefore allow a fluid or slurry, such as cement, to be pumped over long distances without the effect of premature solidification. A wide variety of solidification retarders may be suitable for use in the fluid or slurry compositions used in the present invention. For example, the solidification retarder can include, among other things, phosphonic acid, phosphonic acid derivatives, lignosulfonates, salts, sugars, carbohydrate compounds, organic acids, carboxymethylated hydroxyethylated celluloses, synthetic co- or ter-polymers including sulfonate and carboxylic acid groups and/or borate compounds. In certain embodiments, the solidification retarders used in the present invention are phosphonic acid derivatives, such as described in US Patent 4,676,832, the disclosure of which is incorporated by reference. Examples of suitable borate compounds include but are not limited to sodium tetraborate and potassium pentaborate. Examples of suitable organic acids include gluconic acid and tartaric acid. In general, the solidification retarder is present in the fluid or slurry mixtures used in the present invention in an amount sufficient to delay the solidification time of the fluid or slurry mixture in an underground formation for a desired period of time. More specifically, the solidification retarder may be present in the fluid or slurry compositions used in the present invention in an amount ranging from about 0.1% to about 10% bwoc. In certain embodiments, the solidification retarder is present in the fluid or slurry compositions used in the present invention in the range of from about 0.5% to about 4% bwoc.

The solidification retarders of the present invention may include a sensitizer-containing retarder, such as a boron-containing retarder. The sensitizer can be made of a material with a strong ability to absorb radiation. The sensitizer can also be a scintillator material. The sensitizer can be any material which increases the material's ability to capture ionizing radiation in the slurry. The sensitizer-containing retarder, also referred to as a sensitized retarder, may be a boron-containing retarder, also referred to as a boronated retarder, may include a wide variety of solidification retarders including the solidification retarders described herein, wherein the selected solidification retarder, or combination of solidification retarders, additionally includes at least one boron atom. As discussed in the section immediately preceding, sugars and/or carbohydrates may be used as a retarder in setting a cement mixture. In one embodiment, the retarder is a sensitized sugar or carbohydrate. In a more specific embodiment, the sensitized retarder is boronated glucose. In an even more specific embodiment, the boronated glucose is represented by 3-O-(o-carboranyl-1-ylmethyl)-D-glucose, as presented in US Patent 5,466,679 (Soloway et al).

Various elements can be used as a sensitizer. In general, elements with a larger absorption cross-section than the wellbore treatment fluid mixture can be used to increase the trapping effect of the ionizing radiation in the mixture. Many well treatment fluids may include calcium, which has an absorption cross section for 2200 m/s neutrons of approximately 0.43 ren. A non-limiting listing of elements with an absorption cross-section of 2200 m/s neutrons of 10 children or more is shown below in Table 2. A child is defined as IO"<28>m<2>, and is roughly equivalent to the cross-sectional area of a uranium nucleus .

The mixtures according to the present invention may also include an accelerator. The accelerator helps overcome possible delays caused by the solidification retarders by shortening the solidification time of the fluid or slurry mixture. A wide variety of accelerators may be suitable for use in the fluid or slurry compositions used in the present invention, and the accelerator may include any component that reduces the setting time of a cement mixture. For example, the accelerator may include alkali and alkaline earth metal salts, silicate salts, aluminates, and amines, such as triethanolamine. In one embodiment, the accelerator is a calcium salt. The calcium salt may be selected from the group consisting of calcium formate, calcium nitrate, calcium nitrite and calcium chloride. In a specific embodiment, the accelerator is calcium chloride. The accelerator may be present in the fluid or slurry compositions used in the present invention in an amount from about 0.1% to about 20% bwoc. In certain embodiments, the accelerator is present in the cement compositions used in the present invention in an amount from about 4% to about 12% bwoc.

The accelerators according to the present invention can be combined with a polymer component. In one embodiment, the accelerator is encapsulated by the polymer component. In another aspect, the accelerator is mixed uniformly with the polymer, which serves as a binder, and the resulting mixture is then pressed into a pellet. In yet another aspect, the resulting pellet is finally encapsulated by a polymer component. The polymer component used as a binder during the formation of the pellet may be of a different composition to the polymer component used for encapsulating the pellet. It can also be of a mixture sensitive to alkaline hydrolysis, so that the alkaline environment in the cement system contributes to a faster degradation of the same. The encapsulating polymer layer may be applied using a polymer coating method selected from the group consisting of dip coating, spray coating, extruder coating, surface painting, and any combination thereof. The encapsulating polymer layer can also be applied using any conventional polymer coating method.

The oxidizing agents according to the present invention can be combined with one or more polymer constituents. They may be present in an amount from about 0.05% to about 5% of the fluid or slurry mixture, and capable of attacking any solidification retarder that may be present. In one embodiment, the oxidizing agent is encapsulated by the polymer component. In another aspect, the oxidizing agent is uniformly mixed with the polymer component, which serves as a binder, after which the resulting mixture is pressed into a pellet. In yet another aspect, the resulting pellet is uniformly encapsulated by the polymer component. The polymer component used as a binder in forming the pellet may have a different composition to the polymer component used for encapsulating the pellet and may be selected from a polymer which is particularly resistant to oxidation. Exposure of the fluid or slurry mixture to the ionizing radiation may enable the release of the oxidizing agent which reduces the retarder effect in the retarder and allow solidification.

In one embodiment, the polymer component selected in the present invention is a component of the high alkalinity environment found in cement and exhibits a low tolerance to radiation. In more specific embodiments, the polymer component exhibits a radiation tolerance of less than about 500 KiloGray, optionally less than about 250 KiloGray, optionally less than about 100 KiloGray. Alternatively, the polymer component has a radiation tolerance of about 4 to about 65 KiloGray. A non-limiting listing of polymer degradation upon exposure to ionizing radiation is given in Table 1.

In one aspect, the polymer component is selected from the group consisting of polyisobutylene, fluoroelastomers, silicone rubber, polyesters, polytetrafluoroethylene (PTFE) (available under the trade name TEFLON from E.l. du Pont de Nemours and Company), polyacetals (available under the trade name DELRIN from E.l. du Pont de Nemours and Compoany and under the trade name CELCON from Ticona), polypropylene, copolymers of polypropylene-ethylene, polymethylpentene, fluorinated ethylene-propylene, perfluoroalkoxy (PFA), polymethyl methacrylate (PMMA) and combinations thereof.

Referring to Figures 2 and 3, various polymer films were exposed to a neutron flux of 1.2 x 10<13>/s and tested for embrittlement and gas permeability over time. The film material and thickness were PMMA at 50 micrometers, Delrin at 75 micrometers; PFA at 25 and 12.5 microns and PTFE at 5 microns. Figure 2 illustrates that PMMA with a thickness of 50 micrometres exhibits brittleness at around 18 minutes and at around 50 minutes the film had degraded to an extent where it could no longer be tested. It has also been observed that some materials such as Delrin are more susceptible to radiation degradation than other materials such as PMMA or PFA. The Delrin film with a thickness of 75 microns degrades before the PFA with a thickness of 12.5 microns.

Figure 3 illustrates the effect of film thickness on gas permeability and that the PFA film of 25 micrometer thickness retains gas impermeability for approximately twice as long as a PFA film of approximately 12.5 micrometer thickness exposed to the same radiation. Figure 3 also shows that both PFA films observed gas permeability at an earlier time than when the embrittlement effect was observed, as shown in Figure 2.

Referring to Figure 4, a sample of sodium metasilicate, available as Econilite from Halliburton, was coated with a layer of FluoroPel PFA and with a layer of FluoroPel PAF with B4C. The sample was exposed to a neutron flux of 1.2 x 10<13>/s and tested for conductivity over time. Figure 4 shows that the coating gave a delayed release profile for sodium metasilicate which is relative to the radiation exposure. FluorPel is available from Cytonix corporation.

In another example, a sample of Uranin dye on a glass plate was encapsulated using FluorPel PFA to a thickness of about 36 microns in a container of fluid. The encapsulated dye was exposed to a neutron flux of 1.2 x 10<13>/s for 50 minutes, after which the Uranine dye had produced a visible coloration of the fluid, indicating release into the fluid.

The polymer component may also contain an additional material to promote the degradation of the polymer and/or the release of the accelerator into the fluid or slurry. In one embodiment, a free radical chain scission promoter is added to the polymer capsule and/or polymer component used as a binder to accelerate polymer degradation once it is triggered by exposure to the ionizing radiation. In another embodiment, the polymer component may also contain a sensitizer made of a material with a strong ability to absorb radiation. The promoter or sensitizer can be any material which increases the ability to capture the ionizing radiation in the slurry. In embodiments, the promoter or sensitizing material is a boron compound. In embodiments, the promoter or sensitizer material has a tolerance to ionizing radiation of less than 500 KiloGray.

Methods according to the present invention for isolating a portion of a wellbore may include forming a sealant mixture that includes a solidification modifier, pumping the sealant mixture containing the solidification modifier into a wellbore and exposing the sealant mixture to ionizing radiation after deployment in the wellbore. The solidification modifier according to the invention can be combined with a polymer component. The polymer component may serve to prevent the release of the setting modifier, such as an accelerator, into the sealant composition. The ionizing radiation introduced is sufficient to dissolve, degrade or otherwise break down the polymer component to thereby allow the setting modifier to be released into the sealant composition. Once the setting modifier is released, it is dispersed into and reacts with the sealing compound resulting in the initiation of the setting process. The release of the ionizing radiation, which is under the control of technicians in the field, thus serves as a trigger in initiating the solidification of the sealing compound.

The polymer component can be combined with the solidification modifier by encapsulation, bonding with the solidification modifier in a mixture, or both. The polymer coating used in the method of the present invention can be any polymer component that will degrade upon exposure to ionizing radiation. In one embodiment, the polymer component will degrade upon exposure to gamma radiation. In another embodiment, the polymer component will degrade upon exposure to gamma radiation at a level of less than about 500 KiloGray. In yet another embodiment, the polymer will degrade upon exposure to the ionizing radiation emitted from a gamma ray generator that is also used on oil well logging instruments.

The type and level of ionizing radiation used in the methods of the present invention may vary depending on the polymer component(s) combined with the accelerator. The type and level of the ionizing radiation may depend on what is capable of degrading the polymer component(s). In one embodiment, the type of ionizing radiation includes alpha radiation, beta radiation, gamma radiation, neutron radiation, proton radiation, UV radiation, and X-ray radiation, or combinations thereof. In an optional embodiment, the amount of ionizing radiation required to degrade the polymer component(s) is less than about 500 KiloGray.

Methods according to the present invention for isolating a wellbore may include preparing a sealing mixture that includes a solidification modifier, pumping the sealing mixture containing the solidification modifier into a wellbore and exposing the sealing mixture to ionizing radiation after deployment in the wellbore. The setting modifier according to the invention can be a retarder, optionally a sensitized retarder, such as a boronated retarder. The sensitized retarder according to the invention is sensitive to certain types of ionizing radiation. The ionizing radiation applied is sufficient to dissolve or otherwise break down the retarder, thereby allowing solidification of the sealing compound to proceed.

The type and levels of ionizing radiation used in the methods of the present invention may depend on the type of sensitized retarder used. The type and levels of ionizing radiation used may depend on what is capable of altering or destroying the molecules in the sensitized retarder. In one embodiment, the ionizing radiation source is a high flux neutron source. In a more specific embodiment, the high flux neutron source is selected from the group consisting of plutonium-beryllium, americium-beryllium and americium-lithium. The high flux neutron source is optionally an accelerator-based neutron generator. In one embodiment, the type of ionizing radiation includes one or more of: alpha radiation, beta radiation, gamma radiation, neutron radiation, proton radiation, UV radiation, X-ray radiation, or combinations thereof. In an optional embodiment, the amount of ionizing radiation required to alter or destroy the molecules in the sensitized retarder is less than about 500 KiloGray.

Methods of the present invention for isolating a wellbore may include forming a sealant mixture that includes both an accelerator or oxidizer and a retarder, and exposing the sealant mixture to ionizing radiation. The accelerator or oxidizing agent can be released or activated by exposure of the sealing compound to the ionizing radiation to thereby enable acceleration of the solidification of the sealing compound. The retarder can be altered by exposure of the sealing compound to radiation, so that its ability to retard the solidification of the sealing compound can be hindered.

Methods of the present invention for cementing a wellbore may include the steps of forming a cement mixture that includes hydraulic cement and a sufficient amount of water to form a slurry, adding to the slurry a desired amount of an accelerator or oxidizing agent, pumping the slurry containing the accelerator or the oxidizing agent into a wellbore and exposing the slurry to ionizing radiation after deployment of the slurry in the wellbore. The accelerator or oxidizing agent according to the invention can be combined with a polymer component. The polymer component serves to prevent the release of accelerator or oxidizer into the cement slurry. The ionizing radiation applied is sufficient to dissolve, degrade or otherwise break down the polymer component and thus allow the accelerator or oxidizer to be released into the cement slurry. As soon as the accelerator or oxidizer is released, it is dispersed into the cement slurry and reacts with the slurry or retarder and results in initiation of the setting process. The release of the ionizing radiation, which is under the control of technicians in the field, thus serves as a trigger to initiate the solidification of the cement slurry.

The polymer component may be combined with the accelerator or oxidizing agent by means of encapsulation, bonding with the accelerator in a mixture, or both. The polymer coating used in the methods according to the present invention can be any polymer component which will degrade upon exposure to the ionizing radiation. In one embodiment, the polymer component will degrade upon exposure to gamma radiation. In another embodiment, the polymer component will degrade upon exposure to gamma radiation at a level of less than about 500 KiloGray. In yet another embodiment, the polymer component will degrade from ionizing radiation emitted from a gamma ray generator that is also used on oil well logging instruments.

The type and level of ionizing radiation used in the methods of the present invention may depend on the polymer component(s) combined with the accelerator or oxidizing agent. The type and level of ionizing radiation may depend on what is capable of degrading the polymer component(s). In one embodiment, the type of ionizing radiation includes alpha radiation, beta radiation, gamma radiation, X-ray radiation, or combinations thereof. In an optional embodiment, the amount of ionizing radiation required to degrade the polymer component(s) is less than about 500 Kilogray.

Methods according to the present invention for cementing a wellbore may include the steps of forming a slurry, adding to the slurry a desired amount of retarder, pumping the slurry containing the retarder into the wellbore and exposing the slurry to ionizing radiation after deployment of the slurry in the wellbore. The retarder according to the invention can be a sensitized retarder as described here, such as a boronated retarder. The sensitized retarder according to the invention is sensitive to certain types of radiation. The ionizing radiation applied is sufficient to dissolve or otherwise break down the retarder to thereby allow solidification of the cement slurry to continue.

The type and level of radiation used in the methods of the present invention may depend on the type of sensitized retarder used. The type and level of ionizing radiation used may depend on what is capable of altering or destroying the molecules in the sensitized retarder. In one embodiment, the ionizing radiation source is a high flux neutron source. In more specific embodiments, the high flux neutron source is selected from the group consisting of plutonium-beryllium, americium-beryllium, and americium-lithium. Optionally, the high flux neutron source can be an accelerator-based neutron generator. In one embodiment, the type of ionizing radiation includes alpha radiation, beta radiation, gamma radiation, X-ray radiation, or combinations thereof. In an optional embodiment, the amount of ionizing radiation required to alter or destroy the molecules in the sensitized retarder is less than about 500 KiloGray. In embodiments, the sensitizer may also be a scintillator material.

Methods of the present invention for cementing a wellbore may include the steps of forming a cement mixture that includes hydraulic cement and a sufficient amount of water to form a slurry, adding to the slurry more than the desired amount of a solidification retarder, either conventional or sensitized, and an accelerator or oxidizing agent, pumping the slurry containing the retarder and accelerator into a wellbore and exposing the slurry to ionizing radiation after deployment of the slurry in the wellbore. The accelerator or oxidizing agent according to the invention can be combined with a polymer component. The polymer component serves to prevent the release of the accelerator or oxidizer into the cement slurry. The ionizing radiation supplied is sufficient to dissolve, degrade or otherwise break down the polymer component to thereby allow the accelerator to be released into the cement slurry. As soon as the accelerator or oxidizer is released, it can be dispersed into the cement slurry and react with the slurry or retarder, which initiates the solidification process. The sensitized retarder according to the invention is sensitive to certain types of radiation. The ionizing radiation supplied is sufficient to dissolve or otherwise break down the retarder, thereby allowing solidification of the cement slurry to proceed. The release of the ionizing radiation, which is under the control of technicians in the field, thus serves as a trigger to initiate the solidification of the cement slurry by releasing the accelerator and effecting sufficient alteration or destruction of the retarder.

The type and level of ionizing radiation applied to the cementitious slurry may depend on the procedure used. In processes where an accelerator is added and a solidification retarder is not added, the irradiation should be capable of degrading the polymer component(s) to an extent sufficient to release or otherwise activate the accelerator. In processes where an accelerator is not added and a solidification retarder is added, the ionizing radiation should be capable of altering or destroying the retarder. In some embodiments where an accelerator or oxidizer and a setting retarder are added to the cement slurry, the ionizing radiation will simultaneously degrade the polymer component(s) and destroy the retarder. In other embodiments where an accelerator or oxidizer and a setting retarder are added to the cement slurry, a first source of ionizing radiation is capable of destroying the retarder and a second source of ionizing radiation is capable of degrading the polymer component(s). The first and second source of ionizing radiation can be delivered simultaneously. Alternatively, the source of the ionizing radiation capable of breaking down the polymer component can be delivered first, followed by the source of ionizing radiation capable of destroying the retarder. Alternatively, the source of the ionizing radiation capable of destroying the retarder can be delivered first, followed by the source of the ionizing radiation capable of breaking down the polymer component.

In one embodiment, the setting retarder and/or accelerator or oxidizer is added to the cement mixture before water is added to the mixture. In another embodiment, the setting retarder and/or accelerator or oxidizer is added to the cement mixture after water has been added to the mixture. In yet another embodiment, the solidification retarder is added before the accelerator or oxidizing agent. In yet another embodiment, the accelerator is added before the solidification retarder. In yet another embodiment, the accelerator and/or solidification retarder is added while mixing cement and water.

In one embodiment, as soon as the cementitious mixture containing the solidification retarder and/or accelerator or oxidizing agent has been obtained, the slurry is then placed in the wellbore, such as in an annulus between wellbore and casing. When deploying the slurry containing solidification retarder and/or accelerator or oxidizing agent in the wellbore, the cement particles and the solidification retarder and/or accelerator or oxidizing agent should be mixed substantially evenly with the cement particles in the cement slurry.

In yet another embodiment, a solidification retarder as well as both an accelerator and oxidizing agent are added to the fluid or slurry. Upon exposure to the ionizing radiation, both the accelerator and the oxidizing agent are released. The simultaneous destruction of the retarder by the oxidizing agent and the accelerator in cement hydration of the accelerator results in rapid solidification.

According to embodiments of the invention, the ionizing radiation is applied after the slurry has been placed in the wellbore. Ionizing radiation contains subatomic particles or electromagnetic waves that are sufficiently energetic to release electrons from atoms or molecules, thereby ionizing them. The occurrence of ionization depends on the energy of the penetrating individual particles or waves. An intense stream of particles or waves need not cause ionization if these particles or the following do not carry sufficient energy to be ionizing. In one embodiment, the amount of ionizing radiation introduced into the wellbore is determined by the amount of ionizing radiation required to sufficiently alter the polymer component to allow release of at least a portion of the accelerator or oxidizer. In another embodiment, the amount of ionizing radiation supplied to the wellbore is determined by the amount of ionizing radiation required to sufficiently destroy at least a portion of the retarder. The ionizing radiation can be emitted from charged particles. In one embodiment, the charged particles include alpha particles, beta particles or gamma particles or combinations thereof.

In one embodiment, the ionizing radiation is supplied by an emitter of ionizing radiation located at a point inside the wellbore. In another embodiment, an emitter for ionizing radiation located at the surface emits ionizing radiation directed downwards and into the wellbore. In another embodiment, a radiation source is lowered into the wellbore, such as on a varier, and the ionizing radiation is emitted. The radiation source may be shielded so as not to emit the ionizing radiation otherwise when the shielding is removed. For example, a radiation source can be shielded at the surface when personnel could otherwise be exposed. As soon as the source of ionizing radiation is placed in the wellbore and radiation can be emitted safely, the shielding can be removed or opened, such as by an electronically activated signal transmitted from the surface down the wire to the shielding. In one embodiment, the radiation emitter may emit ionizing radiation while being lowered down the wellbore and while being pulled up along the length of the well. In yet another embodiment, two or more emitters for ionizing radiation are lowered separately to two or more depths, so that two or more depths in the wellbore can be exposed to the ionizing radiation at the same time.

In one embodiment, the ionizing radiation is administered under the control of a technician in the field. The technician, engineer or on-site staff can control the release of the ionizing radiation by triggering a signal that causes a release of the ionizing radiation from an emitter. In this embodiment, the ionizing radiation is released on command from the technician in the field. The ionizing radiation can be released by a control system with parameters such as a timer, flow meter, temperature sensor or similar. In another embodiment, the lowering and/or emission of the ionizing radiation is triggered by a timer mechanism. In yet another embodiment, the lowering and/or emission of the radiation source is triggered

of a flow meter which detects the amount of cement mixture delivered into the well.

As mentioned above, the ionizing radiation for the present invention may be under the control of technicians in the field. The release of the ionizing radiation serves as a trigger in the sense that the radiation can destroy the sensitized retarder, thus allowing solidification of the cement slurry to proceed. The release of the ionizing radiation may also serve as a trigger when the ionizing radiation serves to degrade the polymer component of the accelerator or oxidizer, thereby releasing the accelerator or oxidizer, or both, into the cement slurry. As soon as the accelerator or oxidizing agent is released, it is dispersed into the cement slurry and reacts with the slurry or retarder, causing acceleration of the solidification process. Therefore, technicians in the field can trigger the thickening of the cement slurry. This trigger process puts thickening of the cement slurry under the control of the technician in the field and can result in a reduction in the time required to wait for cement (WOC) during the drilling and completion of a wellbore.

The fluid or slurry mixtures used in the present invention may additionally include a scintillator material. The scintillator material may serve to increase the trapping effect of the ionizing radiation and/or may emit radiation upon exposure to the ionizing radiation. A scintillator material with fluorescent properties can emit radiation, which can be termed secondary radiation, as a result of absorption of radiation from another source. For example, a scintillator material can emit gamma rays, X-rays or UV rays when exposed to neutrons or gamma rays. This secondary radiation can be used to provide radiation to promote the degradation of the polymer and/or the release of the accelerator into the fluid or slurry. If the secondary radiation includes photons or particles with the same wavelength as that of the absorbed radiation, it can be described as resonant radiation.

There are a number of known neutron scintillators, a non-limiting list includes

LiF/ZnS:Ag, Li-glass and Lil:Eu. LiF/ZnS:Ag has been shown to produce a very large neutron multiplier factor and has been measured at 160,000 photons per neutron absorbed where the bulk of the radiation occurs below about 450 nm. Li-glass typically has an emission maximum below approximately 400 nm.

There are a number of known gamma scintillators, and a non-limiting list includes

Nal:TI<+>, Bi4Ge3Oi2(GSO), Gd2SiO5:Ce<3+>, ZnS:Ag. Alkali halides include Csl and Nal. Typical emission maxima observed for some scintillators are: Csl - about 300 nm; BaF2- about 190

to

about 305 nm; CaF2:Eu - about 410 nm; GS0:Ce - about 420 nm; Yttrium Aluminum Perovskite (YAI:CaTi03:Ce) - about 350 nm.

The scintillator can be used in the form of a powder or crystal or with a coating such as

a polymer. Advantages of including scintillators in the fluid or slurry herein

the invention can include local formation of secondary radiation which can minimize the impact from the well casing or other environmental impacts. Potentially large multiplier factors can occur, for example some scintillators will emit more than 10,000 photons for each ionizing radiation particle/photon absorbed. The photons produced by scintillators can be in X-ray and UV spectral regions that can be largely absorbed by the polymer component of the slurry. Since these photons are generated locally by the scintillation, their emission can increase the efficiency of the polymer sheath degradation. More photons above the radical generation limit from the polymer can increase the rate of polymer degradation which can accelerate the rate of thickening of the cement slurry and promote setting initiation behavior.

The scintillator material can be added to the fluid or slurry. The scintillator material may be included in a polymer component that forms an encapsulating layer over particles of an accelerator. The scintillator material can be added to a polymer component that forms a binder for an accelerator that is shaped into a pellet and/or a polymer component that forms an encapsulating layer over the pellet. The scintillator material can also be a sensibility material.

The term "cementitious mixture" which may have been used herein includes pastes (or slurries), mortars and slurries, such as oil well cementing slurries, shotcrete and concrete mixtures including a hydraulic cement binder. The terms "paste", "mortar" and "concrete" are terms of the trade: pastes are mixtures composed of a hydratable (or hydraulic) cement binder (usually, but not exclusively, Portland cement, Masonry cement, Mortar cement and/or gypsum, and may also include limestone , hydrated lime, fly ash, granular slag from incinerators and silica fume or other materials commonly included in such cements) and water; "mortar" is paste which additionally includes fine aggregate (eg sand), and "concrete" is mortar which additionally includes coarse aggregate (eg crushed stone or gravel). The cement mixtures described in this invention are formed by mixing required amounts of certain materials, e.g. a hydraulic cement, water and fine and/or coarse aggregate, which may be required for the production of a specific cementitious mixture.

The term "accelerator" may include any component that reduces the setting time of a cement mixture. For example, the accelerator may include alkali and alkaline earth metal salts, such as a calcium salt. The calcium salt may include calcium formate, calcium nitrate, calcium nitrite or calcium chloride.

The term "encapsulating layer" as used herein can mean any type of coating or bond in which most of the material that is encapsulated is contained therein and the dispersion of the material is substantially limited by the layer. It does not mean that all material that is encapsulated is contained within the layer or that the material that is encapsulated cannot leak out through the encapsulation layer.

The term "oxidant" or "oxidizing agent" may include any component capable of degrading the retarder present. These include but are not limited to alkaline earth salts and zinc salts of peroxide, perphosphate, perborate, percarbonate; calcium peroxide, calcium perphosphate, calcium perborate, magnesium peroxide, magnesium perphosphate, zinc perphosphate; calcium hypochlorite, magnesium hypochlorite, chloramine T, trichloroisocyanuric acid, trichloromelamine, dichloroisocyanurate dihydrate, anhydrous cycloisocyanurate and mixtures thereof.

The term "radiation tolerance" as used herein is the amount of ionizing radiation that a material can withstand without noticeable or measurable degradation.

The term "retarder" or "set retarder" may include boronated or non-boronated forms of phosphonic acid, phosphonic acid derivatives, lignosulfonates, salts, sugars, carbohydrate compounds, organic acids, carboxymethylated hydroxyethylated celluloses, synthetic co- or ter-polymers including sulfonate and carboxylic acid groups and/or borate compounds.

The term "ionizing radiation" or "radiation" can be defined as the induction of ionization or indirect ionization capable of releasing electrons from atoms or molecules and can include alpha radiation, beta radiation, gamma radiation, neutron radiation, proton radiation, UV and X-ray radiation.

The term "solidify" as used herein refers to an increase in mechanical strength of a fluid or slurry sufficient to effect a desired result, such as to restrict movement of an object or to prevent fluid flow or pressure transfer, regardless of whether the cement has hardened to a completely solid mixture. A fluid or slurry can be said to be solidified when it has solidified to a sufficient level to achieve the desired result, such as isolating a specific zone or limiting fluid flow or pressure transfer, regardless of whether it has reached its final consistency.

The term "well treatment fluid" may be any fluid or slurry suitable for well operations, drilling, completion, workover or production operations such as cement, solidifiable drilling muds, lost circulation fluids, fracturing fluids, structural fluids, sealants, resins, etc. and combinations thereof.

Depending on the context, all references to the "invention" herein may in some cases refer only to certain specific embodiments. In other cases, reference may be made to subjects reproduced in one or more of the requirements, but not necessarily all. While the above is directed to embodiments, versions and examples of the present invention, which are included to enable a person of ordinary skill in the art to practice the invention when the information in this document is combined with available information and technology, the invention is not limited to only these specific embodiments, versions and examples. Other and further embodiments, versions and examples of the invention can be provided without deviating from the basic idea thereof and the scope is determined by the subsequent patent claims.

While compositions and methods are described as "comprising," "containing," or "including" various components or steps, the compositions and methods may also "consist principally of" or "consist of" the various components and steps. All numbers and intervals described above may vary to a certain extent. When a numerical interval with lower and upper bounds is described, any number and any included interval is considered to lie within the interval specifically described. In particular, any interval of values (in the form "from about a to about b" or equivalently "from about a to b", "from about a-b") described here shall be interpreted as illustrating any number and interval that falls within the wider interval of values. Designations in the requirements also have their clear and ordinary meaning, unless otherwise expressly and clearly stated.

Claims (91)

1. Procedure for use in a wellbore comprises the steps of placing a mixture in an underground formation after drilling the wellbore therein and exposing the mixture to ionizing radiation. 2. Method according to claim 1 for isolating a part of a wellbore where the mixture is a sealing mixture. 3. Method according to claim 2, whereby the step of exposing the mixture to the ionizing radiation initiates solidification of the sealing mixture. 4. Method according to claim 2 or 3, additionally comprises: preparation of the sealing mixture which comprises a solidification modifier; whereby the step of exposing the sealing compound to the ionizing radiation changes the setting modifier. 5. Method according to claim 4, whereby the solidification modifier is selected from the group consisting of an accelerator, an oxidizing agent, a solidification retarder and combinations thereof. 6. A method according to claim 5, wherein the step of exposing the solidification mixture to the ionizing radiation enables the solidification modifier to react to increase the mechanical strength of the sealing mixture. 7. Method according to one of claims 1 to 6, whereby the mixture is selected from the group consisting of a resin, a cement, a solidifiable sludge, fluid for lost circulation and/or a structural fluid. 8. Method according to one of claims 4 to 7, whereby the solidification modifier comprises a polymer component. 9. Method according to claim 8, whereby the ionizing radiation causes degradation of the polymer component. 10. Method according to claim 8 or 9, whereby the polymer component forms an encapsulating layer over the particles with solidification modifier. 11. Method according to one of claims 8 to 10, whereby the polymer component is mixed with the solidification modifier, whereby the polymer component serves as a binder and the resulting mixture is formed into a pellet. 12. Method according to claim 11, whereby the polymer component forms an encapsulating layer over the pellet. 13. Method according to claim 11 or 12, whereby a first polymer component acts as a binder which is exposed to alkaline hydrolysis and a second polymer component forms an encapsulating layer over the pellet which is resistant to alkaline hydrolysis. 14. Method according to one of claims 8 to 13, whereby the polymer component degrades after being exposed to the ionizing radiation. 15. Method according to one of claims 8 to 14, whereby the polymer component has a radiation tolerance of less than approximately 500 KiloGray. 16. Method according to one of claims 8 to 15, whereby the polymer component is selected from the group consisting of polyisobutylene, fluoroelastomers, silicone rubber, polyesters, polytetrafluoroethylene, polyacetals, polypropylene, copolymers of polypropylene-ethylene, polymethylpentene, polymethyl methacrylate, fluorinated ethylene propylene and combinations thereof. 17. Method according to one of claims 4 to 16, whereby the solidification modifier comprises an accelerator added in an amount from approximately 0.1% to approximately 20% of the weight of the sealing mixture. 18. Method according to one of claims 4 to 17, whereby the solidification modifier comprises a solidification retarder added in an amount from about 0.1% to about 10% of the weight of the sealing mixture. 19. Method according to one of claims 4 to 18, whereby the solidification modifier comprises an oxidizing agent added in an amount from about 0.05% to about 5% of the weight of the sealing mixture. 20. A method according to one of claims 6 to 19, wherein the step of exposing the sealing compound to the ionizing radiation enables an oxidizing agent to degrade a retarder and reduce its retarding effect. 21. Method according to one of claims 5 to 20, whereby the solidification modifier comprises a sensitized retarder. 22. Method according to claim 21, whereby the sensitized retarder is a boronated compound. 23. Method according to claim 21 or 22, whereby the ionizing radiation is sufficient to degrade and reduce the retarding effect of the solidification retarder. 24. Method according to one of claims 1 to 23, whereby it includes at least one sensitivity material to increase the ability of the mixture to capture the ionizing radiation. 25. Method according to claim 24, whereby the sensitivity material comprises a boron compound. 26. Method according to one of claims 1 to 25, whereby the mixture additionally comprises at least one scintillator material capable of emitting secondary radiation upon exposure to the ionizing radiation. 27. Method according to claim 26, whereby the scintillator material is selected from the group consisting of LiF/ZnS:Ag, Li-glass and Lil:Eu, Nal:TI<+>, Bi4Ge3012(GSO), Gd2Si05:Ce3+, ZnS:Ag, Csl , Nal, BaF2, CaF2:Eu, GSO:Ce,YAI:CatiO3:Ce and combinations thereof. 28. Method according to one of claims 1 to 27, whereby the ionizing radiation is selected from the group consisting of alpha radiation, beta radiation, gamma radiation, neutron radiation, proton radiation, UV radiation, X-ray radiation and combinations thereof. 29. Method according to one of claims 1 to 28, whereby the ionizing radiation is emitted from a neutron source with a high flux. 30. Method according to claim 29, whereby the high flux neutron source is selected from the group consisting of plutonium-beryllium, americium-beryllium, americium-lithium and combinations thereof. 31. Method according to claim 29, whereby the high-flux neutron source is an accelerator-based neutron generator. 32. Method according to claim 1 for cementing a well hole, whereby the mixture is a cement mixture comprising: hydraulic cement, an accelerator, and a sufficient amount of water to form a slurry; and whereby the ionizing radiation activates solidification of the cement mixture. 33. Method according to claim 32, whereby it comprises a sensitivity material to increase the ability of the cement mixture to capture the ionizing radiation. 34. Method according to claim 33, whereby the sensitivity material comprises a boron compound. 35. Method according to claim 32, 33 or 34, whereby the accelerator is combined with a polymer compound. 36. Method according to claim 35, whereby the ionizing radiation causes degradation of the polymer compound. 37. Method according to one of claims 32 to 36, whereby the amount of accelerator added is an amount from approximately 0.1% to approximately 20% of the cement weight. 38. Method according to claim 35, 36 or 37, whereby the polymer compound forms an encapsulating layer over the particles with accelerator. 39. Method according to one of claims 35 to 38, wherein the polymer component is mixed with the accelerator, wherein the polymer component serves as a binder and the resulting mixture is then formed into a pellet. 40. Method according to claim 39, whereby the polymer component forms an encapsulating layer over the pellet. 41. Method according to one of claims 35 to 40, whereby a first polymer component serves as the binder which is exposed to alkaline hydrolysis and a second polymer compound which forms an encapsulating layer over the pellet which is resistant to alkaline hydrolysis. 42. Method according to one of claims 35 to 41, whereby the polymer component is degraded after being exposed to the ionizing radiation. 43. Method according to one of claims 35 to 42, whereby the polymer component has a radiation tolerance of less than approximately 500 KiloGray. 44. Method according to one of claims 35 to 43, whereby the polymer component is selected from the group consisting of polyisobutylene, fluoroelastomers, silicone rubber, polyesters, polytetrafluoroethylene, polyacetals, polypropylene, copolymers of polypropylene-ethylene, polymethylpentene, polymethyl methacrylate, fluorinated ethylene propylene and combinations thereof. 45. Method according to one of claims 32 to 44, whereby it comprises at least one scintillator material capable of emitting secondary ionizing radiation upon exposure to the ionizing radiation. 46. Method according to claim 45, whereby the scintillator material is selected from the group consisting of LiF/ZnS:Ag, Li-glass and Lil:Eu, Nal:TI<+>, Bi4Ge3012(GSO), Gd2Si05:Ce<3+>, ZnS: Ag, Csl, Nal, BaF2, CaF2:Eu, GSO:Ce,YAI:CaTi03:Ce and combinations thereof. 47. Method according to claim 1 for cementing a wellbore, wherein the mixture is a cement mixture comprising: hydraulic cement, a sufficient amount of water to form a slurry, and a solidification retarder; and whereby the ionizing radiation degrades the solidification retarder. 48. Method according to claim 47, whereby the solidification retarder is a sensitized retarder. 49. Method according to claim 48, whereby the sensitized retarder is a boronated compound. 50. Method according to claim 47, 48 or 49, whereby the ionizing radiation is sufficient to degrade the retarder and allow the cement mixture to solidify. 51. Method according to one of claims 47 to 50, whereby solidification retarders are added in an amount from approximately 0.1% to approximately 10% of the cement weight. 52. Method according to one of claims 47 to 51, whereby the ionizing radiation is emitted from a neutron source with a high flux. 53. Method according to one of claims 47 to 52, whereby the high flux neutron source is selected from the group consisting of plutonium-beryllium, americium-beryllium, americium-lithium and combinations thereof. 54. Method according to one of claims 47 to 53, whereby the high-flux neutron source is an accelerator-based neutron generator. 55. Method according to one of claims 47 to 54, whereby it comprises a scintillator material capable of emitting secondary radiation upon exposure to the ionizing radiation. 56. Method according to claim 55, whereby the scintillator material is selected from the group consisting of LiF/ZnS:Ag, Li-glass and Lil:Eu, Nal:TI<+>, Bi4Ge3012(GSO), Gd2Si05:Ce<3+>, ZnS: Ag, Csl, Nal, BaF2, CaF2:Eu, GSO:Ce,YAI:CaTi03:Ce and combinations thereof. 57. The method of claim 1 for cementing a wellbore, wherein the component is a cement mixture comprising: hydraulic cement, sufficient water to form a slurry, a solidification retarder, and an additive selected from the group consisting of an accelerator, an oxidizing agent, and combinations thereof of these; and whereby the ionizing radiation separately or in combination deactivates the solidification retarder, activates the accelerator or releases the oxidizing agent. 58. Method according to claim 57, whereby the ionizing radiation that is supplied is sufficient to degrade the retarder and allow the cement mixture to solidify. 59. Method according to claim 57 or 58, whereby the cement mixture additionally comprises a polymer component. 60. Method according to claim 59, whereby the ionizing radiation causes the degradation of the polymer component. 61. Method according to claim 59 or 60, wherein the polymer component is a binder, an encapsulating layer, or both, which inhibits the release of the accelerator and/or an oxidizing agent. 62. A mixture comprising: a well treatment fluid, and a solidification modifier; whereby the solidification modifier is capable of being degraded upon exposure to ionizing radiation. 63. Mixture according to claim 62, whereby it is a sealing mixture. 64. A mixture according to claim 62 or 63, whereby the degraded solidification modifier serves to increase the mechanical strength of the sealing mixture. 65. A mixture according to claim 62, 63 or 64, whereby the setting modifier is selected from the group consisting of a sensitized retarder, an accelerator combined with a polymer component, an oxidizing agent combined with a polymer component and combinations thereof. 66. Mixture according to one of claims 62 to 65, wherein the solidification modifier has a radiation tolerance of less than about 500 KiloGray. 67. A mixture according to claim 62, which is a cement mixture whereby the well treatment fluid comprises: hydraulic cement and water; and wherein the solidification modifier comprises a sensitized retarder. 68. A mixture according to claim 67, wherein the sensitized retarder is a boronated compound. 69. Mixture according to claim 67 or 68, whereby the sensitized retarder has a radiation tolerance of less than about 500 KiloGray. 70. Mixture according to claim 67, 68 or 69, whereby the amount of retarder added is in an amount from approximately 0.1% to approximately 10% of the weight of the cement. 71. Mixture according to one of claims 67 to 70, whereby it additionally comprises at least one scintillator material capable of emitting secondary radiation upon exposure to the ionizing radiation. 72. Mixture according to one of claims 67 to 71, whereby the scintillator material is selected from the group consisting of LiF/ZnS:Ag, Li-glass and LihEu, Nal:TI<+>, Bi4Ge3Oi2(GSO), Gd2Si05:Ce<3+>, ZnS:Ag, Csl, Nal, BaF2, CaF2:Eu, GSO:Ce,YAI:CaTi03:Ce and combinations thereof. 73. A mixture according to claim 62 which is a cement mixture, whereby the well treatment fluid comprises hydraulic cement and water; and wherein the solidification modifier comprises an accelerator or an oxidizing agent, or both, wherein the accelerator and/or oxidizing agent is combined with at least one polymer component; whereby the polymer component is capable of being degraded upon exposure to ionizing radiation. 74. Mixture according to claim 73, whereby accelerator is added in an amount from approximately 0.1% to approximately 20% of the cement weight. 75. Mixture according to claim 73 or 74, whereby the oxidant is added in an amount from about 0.05 to about 5% of the cement weight. 76. Mixture according to one of claims 73 to 75, whereby both an accelerator and an oxidant are added in amounts from approximately 0.01% to approximately 20% and approximately 0.05% to approximately 5% of the cement weight, respectively. 77. Mixture according to one of claims 73 to 76, whereby the polymer component forms an encapsulating layer over the accelerator particles. 78. Mixture according to one of claims 73 to 77, whereby the polymer component is mixed with the accelerator and/or oxidizing agent, whereby the polymer component serves as a binder and the resulting mixture is then pressed into a pellet. 79. Mixture according to claim 78, whereby the polymer component forms an encapsulating layer over the pellet. 80. Mixture according to claim 78 or 79, whereby a first polymer component serves as a binder which is exposed to alkaline hydrolysis and a second polymer compound which forms an encapsulating layer over the pellet which is resistant to alkaline hydrolysis. 81. Mixture according to one of claims 73 to 80, whereby the polymer component has a radiation tolerance of less than about 500 KiloGray. 82. Mixture according to one of claims 73 to 81, whereby it comprises at least one scintillator material capable of emitting secondary radiation upon exposure to the ionizing radiation. 83. Mixture according to claim 82, whereby the scintillator material is selected from the group consisting of LiF/ZnS:Ag, Li-glass and Lil:Eu, Nal:TI<+>, Bi4Ge3Oi2(GSO), Gd2Si05:Ce<3+>, ZnS: Ag, Csl, Nal, BaF2, CaF2:Eu, GSO:Ce,YAI:CaTi03:Ce and combinations thereof. 84. Mixture according to one of claims 73 to 83, whereby the oxidizing agent is encapsulated separately in a polymer material resistant to oxidation under the prevailing environment. 85. A mixture according to claim 62 which is a cement mixture, whereby the well treatment fluid comprises: hydraulic cement and water; and wherein the solidification modifier comprises: a sensitized retarder; and an accelerator combined with a polymer component; whereby the sensitized retarder and polymer component are capable of being degraded upon exposure to ionizing radiation. 86. Mixture according to claim 85, whereby retarders are added in an amount from approximately 0.1% to approximately 10% of the weight of the cement. 87. Mixture according to claim 85 or 86, whereby the accelerator is added in an amount from approximately 0.1% to approximately 20% of the cement weight. 88. Mixture according to one of claims 85 to 87, whereby the polymer component has a radiation tolerance of less than about 500 KiloGray. 89. Mixture according to one of claims 85 to 88, whereby the polymer component forms an encapsulating layer over the accelerator particles. 90. A mixture according to one of claims 85 to 89, wherein the polymer component is mixed with the accelerator and the resulting mixture is then pressed into a pellet. 91. Mixture according to claim 90, whereby the polymer component forms an encapsulating layer over the pellet.